1. Field of the Invention
The present invention relates to a wiring apparatus making an electrical connection between a steering wheel and a steering column of a motor vehicle, which rotatably houses a steering shaft, having the steering wheel mounted to its upper end, and inserted into the steering column.
2. Description of the Related Art
FIG. 11 is a sectional view of a steering apparatus of a motor vehicle into which the conventional wiring apparatus is incorporated. As shown in FIG. 11, a steering column tube 2 fixed to a car body is housed in a steering cover 1, and a turn signal box 3 is mounted to an outer periphery on an upper end of the steering column tube 2. A steering shaft 4 is rotatably supported through a bearing 5 in the steering column tube 2. A steering wheel 6 is fixed to the upper end of the steering shaft 4, whose lower end is inserted into a steering gear box (not shown).
A wiring apparatus 7 is disposed between the steering wheel 6 and the turn signal box 3. The wiring apparatus 7 comprises a metallic contact ring 8 fixed to the steering wheel 6 and a metallic piece 9 fixed to the turn signal box 3. The contact ring 8 is fixed to a back face of the steerinG wheel 6 and the steering shaft 4 is inserted into a hole made in a center of the contact ring 8. On the other hand, the metallic piece 9 has its base end fixed to the turn signal box 3 and its top end contacted with the contact ring 8 by the spring force of the metallic piece 9. Thus, the metallic piece 9 is always in contact with the contact ring 8 without being influenced by rotational operations of the steering wheel 6.
A horn switch 10 is provided in a center of the steering wheel 6. A traveling contact 11 of the horn switch 10 is electrically connected to the contact ring 8 by way of a lead wire 13, and a lead wire 14 connected to a fixed contact 12 of the horn switch 10 is led into the steering shaft 4. A lead wire 15 connected to the metallic piece 9 and the lead wire 14 are connected with a battery, a horn and the like, respectively, to constitute a horn circuit.
In the steering apparatus, when a driver pushes the horn switch 10 so that both the contacts 11 and 12 are closed, the horn circuit is correspondingly closed. As a result, a current flows in the lead wire 15, the metallic piece 9, the contact ring 8, the lead wire 13, the traveling contact 11, the fixed contact 12 and the lead wire 14, thereby sounding a horn.
In the conventional wiring apparatus 7, however, since a connection between the metallic piece 9 and the contact ring 8 will permit a flow of the current, if any dust comes between the contact ring 8 and the metallic piece 9, an imperfect contact results. For this reason, there is a difficulty in obtaining function of stably supplying the current.
As a similar wiring apparatus for making an electrical wiring between the steering wheel and the steering column, a mechanism as mentioned in Japanese Utility Model Laying Open Gazette 57-48173 is known. In that case, the similar difficulty is also incurred.
FIG. 12 is a schematically sectional view of another conventional wiring apparatus 20 as disclosed in Japanese Utility Model Laying Open Gazette 63-137069. As shown in FIG. 12, the wiring apparatus 20, connecting an inner-side case 21 and an outer-side case 22 to each other such that these two cases 21 and 22 can be relatively rotated, has a ring-shaped housing space 23 surrounded by both the cases 21 and 22. A flexible wire of metal 24 is housed in the housing space 23. The flexible wire 24, spirally wound, has an outer-side end fixed to the outer-side case 22 and an inner-side end fixed to the inner-side case 21. The outer-side case 22 is fixed to a steering column, while the inner-side case 21 is fixed to a steering wheel. Thus, the flexible wire 24 permits the electrical connection between the steering wheel and the steering column to be effected. In the wiring apparatus 20 of such a construction, for example, if operations of the steering wheel cause the inner-side case 21 to be rotated in a clockwise direction of FIG. 12, the flexible wire 24 is wound to decrease its diametrical dimension, whereas if the inner-side case 21 is rotated reversively in a counterclockwise direction of FIG. 12, the diametrical dimension of the flexible wire 24 is increased to release its winding. Thus, the supply of the current between the steering column and the steering wheel is ensured by permitting a rotation of the steering wheel while adjusting the wound state of the flexible wire 24.
In the wiring apparatus 20, since the electrical connection between the steering column and the steering wheel is made directly by the flexible wire 24 instead of a contact touch construction as shown by the conventional example of FIG. 11, the stable supply of the current can be assured. However, since the rotation of the steering wheel is permitted by an adjustment of winding amount of the flexible wire 24, which is wound in one direction only, the diametrical dimension of the flexible wire 24 changes in response to the rotational operations of the steering wheel. As a result, it is necessary to design a dimension of the outer-side case 22 on the basis of the maximum diametrical dimension of the flexible wire 24, and therefore it may give rise to size problems.
In addition, whenever a repetitiOn of the winding action and the releasing actiOn of the wound state of the flexible wire 24 is caused by the rotational operations of the steering wheel, a stress concentrates in bent parts 24a and 24b in the vicinity of both the ends of the flexible wire 24. For this reason, the wiring apparatus 20 has a problem of deteriorating durability due to an accumulation of the fatigue in the bent parts 24a and 24b.